b) Description of the Related Art
Dimethyl sulfone (also known as methylsulfonylmethane, MSM, and DMSO2), the oxidized form of dimethyl sulfoxide, is a well-known natural health product (Jacob, S. W.; Lawrence, R. M.; Zucker, M. The Miracle of MSM, New York: Berkley Books, 1999). Its uses have been described in several patents, including as a dietary sulfur supplement (U.S. Pat. No. 4,616,039), as a treatment for parasite infections (U.S. Pat. No. 4,914,135), as a pharmaceutical carrier (U.S. Pat. No. 4,468,547), and as a food additive (U.S. Pat. No. 5,071,878).
Known processes for the preparation of dimethyl sulfone from dimethyl sulfoxide utilize assorted catalysts, including a molybdate catalyst in the presence of sulfuric acid. The process requires the use of glass-lined reactors, the neutralization of acid components, and the caustic decomposition of hydrogen peroxide prior to product isolation and, therefore, results in the generation of salt by-products. Isolation of the dimethyl sulfone requires high vacuum and high temperature. The final product is flaked to obtain a flowing solid material.
U.S. Pat. No. 3,069,471 describes a process for preparing sulfones by the slow addition of hydrogen peroxide to the corresponding sulfoxide. Although this method avoids catalysts and organic solvents, it produces small amounts of acidic by-products. In addition, the process requires close monitoring of the hydrogen peroxide concentrations and the amount of water present in the reaction vessel in order to avoid explosive decomposition of the hydrogen peroxide.
Japanese Patent 79 44,611 similarly describes the production of dimethyl sulfone and is subject to the same limitations as U.S. Pat. No. 3,069,471.
Because dimethyl sulfone is used as a health product, it is desirable to have a process for making the material in pure form without the use of added catalyst and which results in limited or no by-product formation.
The present invention provides a process for preparing dimethyl sulfone by the oxidation of dimethyl sulfoxide using hydrogen peroxide, without the necessity of added catalysts. The process also accommodates the use of naturally-derived dimethyl sulfoxide from pine tree process and dimethyl sulfoxide derived from petroleum sources such as sour gas wells. The process comprises the steps of: a) simultaneously adding dimethyl sulfoxide and an aqueous solution of hydrogen peroxide to a pre-heated heel of aqueous dimethyl sulfone in the smaller of two reaction vessels at a rate sufficient to maintain the reactor at or below 120xc2x0 C. during the exothermic reaction; b) transferring the partially-reacted mixture into a larger reaction vessel where the reaction is completed by the continued simultaneous charging of the raw materials; c) distilling water from the mixture contained in the larger reactor during the reaction; and d) isolation of the final product as either a free-flowing, crystallized solid by filtration or centrifugation or as a flaked solid by distillation and flaking.
It is an object of this invention to provide pure, crystalline (or flaked), flowable dimethyl sulfone suitable for administration to humans.